1. Field of the Invention
This invention relates to a contacts material for a vacuum valve of improved breaking performance.
2. Description of the Related Art
Apart from the fundamental three performance requirements: anti-welding property, voltage withstanding capability and current interrupting property, the characteristics required for contacts materials for vacuum valves include as important requirements low and stable rise in temperature and low and stable contacts resistance. However, some of these requirements are mutually antagonistic, so it is difficult to satisfy all the requirements by a single metal. In the many contacts materials which have been implemented, contacts materials have therefore been developed by combining two or more elements so as to mutually complement the deficiencies of each others performance, and to meet specific applications such as large current use or high withstanding voltage use, and they have excellent characteristics in their own way. However, performance in respect of increasingly severe requirements still leaves something to be desired.
For example, in contacts materials for the vacuum valve for general-use circuit breakers, in initial development of vacuum valves, anti-welding property was emphasized. It was therefore the practice to add a welding preventing constituent such as Te or Bi in the amount of not more than 10 weight %, with Cu as main constituent (see for example issued Japanese Patent Publication (Kokoku) Nos. Sho. 41-12131, Sho. 44-23751). However, with demands such as increase in the field of use, miniaturization and price reduction of vacuum circuit breakers and vacuum valves, contacts having breaking performance better than that of the conventional Cu--Te or Cu--Bi contacts have come to be demanded. As a result, Cu--Cr contacts, which have better breaking performance than conventional contacts, have come to be the most common. Nevertheless, the present situation is that contacts having even better breaking capability are being demanded.
The reason why Cu--Cr contacts have better breaking performance than Cu--Bi or Cu--Te contacts is thought to be that the arc-proof material Cr has a getter action, and that the getter action can be displayed to advantage since Cr can easily form a plasma vapor, due to its appropriate vapor pressure and melting point.
With this in view, the inventors carried out breaking tests on contacts materials manufactured by a sintering method or melting method using conductive constituents and arc-proof materials such as Ti, Zr, V, or Y having a larger getter action than Cr and a more appropriate vapor pressure and melting point than CF. In the JEC4 test, here JEC is the abbreviation for Japan Electrotechnical Committee Standard, of repeated contact closure and contact opening, better performance was obtained than with the conventional Cu--Cr contacts. However, in the JEC5 test, in which breaking is performed after passing current for a fixed time, good performance was not obtained, in that welding tended to occur. It would therefore be difficult to say that sufficient breaking performance is obtained with this concept, alone, and reliability was lacking.